James Frey: 'the product of a culture with a short memory and a skewed moral sense'. Photograph: Antonio Olmos/ Antonio Olmos

"James Frey," according to the hype for this novel about Christ's second coming in New York City, "is not like other writers." The marketers mean to imply that he is exalted above his terrestrial colleagues by his sufferings: arrest, abuse, exile, public contempt. Frey is, we are to understand, a man of sorrows, who has undergone excruciation if not crucifixion, and has been stigmatised by his bad press.

The truth is paltrier and more profane. Frey happens to be a shameless faker, who manufactures mishaps to embellish his personal mystique. In A Million Little Pieces, his memoir about his supposed crack addiction, he claimed to have knocked down a Michigan cop while high, after which he allegedly brawled with a platoon of beefy officers who hurled him into jail for three months; it turned out that he was merely involved in a minor collision, behaved with exemplary sobriety at the police station, and was released a few hours later. Harried by Oprah Winfrey, Frey admitted that the confessional memoir was a tissue of fibs, but isn't that, he asked, what fiction means? Others were less impressed by his flippant irony. His agent sacked him, and his publisher shrewdly reneged on a seven-figure advance for two more books. Customers who felt defrauded sued, and were sent refunds.

All this was a mere five years ago; now Frey is back, unredeemed, assuming the persona of a divine con artist who is his fancied alter ego. "He's been called a saviour, a revolutionary, a genius," the publicists declare. Of course, they admit, he has also been fingered as a mythomaniac trickster. But couldn't the same be said of Christ, who in the new novel is, like Frey, martyred by the media? It's a feat of stupefying impudence: if only there were a God able to strike the imposter down during his tour of the talk shows! But Frey is the product of a culture with a short memory and a skewed moral sense. He's also less a writer than a professional celebrity, which means that he can count on being rewarded for behaving badly.

This current crock of mendacity is a "high-concept" fabrication, artlessly crass in its retelling of what's meant to be the greatest story ever told. Christ returns to Earth, to get us ready for the annihilation of our vile, belligerent species. Renamed Ben Zion, he joins a band of apocalyptic loons who hole up in the subway tunnels beneath Manhattan. His divinity seems to be proved when he miraculously survives an accident on a building site after a sheet of glass punctures his skull and severs his arteries. He communes with his heavenly father during epileptic seizures, and gathers around him a gaggle of hapless apostles, to whom he preaches drippy sermons about peace. He licks and laps the genitalia of his female acolytes, disseminating celestial bliss in their nether regions; bouts of tantric sex follow, along with vegetarian love-ins at a rural commune.

The FBI arrest him as a menace to public order and – since nailing felons to a cross is not an option in the squeamish US – a court prescribes a lobotomy. Reduced to idiocy but still alive, he is spared the bother of having to resurrect himself, and instead simply vanishes. "I love you," one of his concubines burbles three times on the last page, perhaps hoping that her credulity will be contagious.

In effect Ben Zion abolishes himself by disparaging the notion of a deity who is incarnate. "I was just part of this greater thing, or place, or force, or energy," he drivels, like a semi-articulate hippy. In saying this he rescinds the literary gift of the Christian story, which is its consecration of all that is humble, modest, earthy – the minutiae of carpentry and money-lending, of loaves and fishes, of nails and thorns and cups containing vinegar not water. This astral blather dispenses Frey from having to convince us that his would-be god is a real human being. Instead the aesthetics of fiction, so cleverly elaborated when he planned the imposture of A Million Little Pieces, come to his aid: Ben Zion admiringly defines religion as "a beautiful con, the longest running fraud in human history". As Frey's surrogate, he exposes his own dishonesty while blaming those who he duped for being so gullible. A disciple backs him up by arguing that "the sin of lying was not actually a sin", since all human beings do whatever they please and then invent justifications.

It might all possess a witty, teasing effrontery if Frey were a better writer. Matthew Arnold told the sceptical Victorians to read the Bible for its poetry; Frey, however, is lumpenly prosaic, unable to conceive of or communicate rapture. "God is what you feel when there's love in your heart," says one of the converts. "It's an awesome feeling." Someone else avows that "Nothing in the world is more beautiful than a child's smile": Oprah, I predict, will forgive Frey's previous trespasses when she reads that mawkish sentence.

The huffing and puffing publicists prescribe our responses to the book: "Be moved, be enraged, be enthralled by this extraordinary masterpiece," they command. But take it from me: The Final Testament of The Holy Bible is blandly unmoving. You'll be irritated not enraged, and will find its thraldom easy to resist. Extraordinary masterpiece? Well, let's just say it makes Jesus Christ Superstar sound like Handel's Messiah.